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SubjectRe: Async suspend-resume patch w/ completions (was: Re: Async suspend-resume patch w/ rwsems)
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On Sunday 20 December 2009, Alan Stern wrote:
> On Sat, 19 Dec 2009, Rafael J. Wysocki wrote:
>
> > On Friday 18 December 2009, Alan Stern wrote:
> > > On Fri, 18 Dec 2009, Rafael J. Wysocki wrote:
> > >
> > > > I didn't manage to do that, but I was able to mark sd and i8042 as async and
> > > > see the impact of this.
> > >
> > > Apparently this didn't do what you wanted. In the nx6325
> > > sd+i8042+async+extra log, the 0:0:0:0 device (which is a SCSI disk) was
>
> To be precise, the device is an ATA or SATA disk but it is managed by
> the sd driver.
>
> > > suspended by the main thread instead of an async thread.
> >
> > Hm, that's odd, because there's a noticeable time difference between the
> > two cases in which the sd is sync and async. I'll look into it further.
>
> I don't know what the whole story is, but the PID number tells the
> tale.
>
> > > There's an important point I neglected to mention before. Your logs
> > > don't show anything for devices with no suspend callbacks at all.
> > > Nevertheless, these devices sit on the device list and prevent other
> > > devices from suspending or resuming as soon as they could.
> >
> > Unless they are async, that is.
>
> Yes. It would be simpler to make them async. But first we ought to
> know what they are. Can you add an extra line to the log for such
> devices?

Sure, I'll do that.

> What I'm afraid of is that there might be a "normal" device with a
> "normal" ancestor but with "abnormal" devices in between (where
> "normal" means there is a suspend or resume routine and "abnormal"
> means all the method pointers are NULL). I know that this happens when
> there's a USB mass-storage device, for example. If we complete the
> intermediate devices immediately, then there won't be anything to
> prevent the ancestor from suspending before the device or the device
> from resuming before the ancestor.

I'm afraid of that too.

Rafael


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